Thermal conductivity detector geometry

Figure 5.6. Typical geometry of a thermal conductivity detector cell. The feedthroughs supporting the axial filament are insulated from the stainless steel body by alumina ceramic. All dimensions are in centimeters. ...

The standard thermal conductivity detector employed by Varian is a Y-geometry 140 yi cell consisting of four matched filaments arranged in a Wheatstone bridge configuration and operated in the constant mean temperture mode. The cell was replaced by a 30ul TCD and the electronics were modified to compensate for change in filament resistance. 

Thermal conductivity is the flow of heat from a body at a higher temperature to an accepting material. The flow of heat is dependent on the cross-sectional area, temperature, temperature coefficient and geometry of the donor body, and the nature and cross-sectional area of the accepting material. The TCD signal is therefore highly dependent on cell design and is also directly proportional to the concentration, C, and velocity, Fmol> of the analyte molecules in the detector, the temperature difference, AT, between the hot filament and the cell, and is inversely proportional to the specific heat, Cy, of each analyte ... 

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